Method for shucking lobster, crab or shrimp

ABSTRACT

A method for facilitating the removal of the shell of a lobster, crab or shrimp by exposing the lobster, crab or shrimp to pressure for a period of time sufficient to effect detachment of the meat from the shell. Following pressurization, the shell can be easily removed using any available means to provide deshelled raw lobster, crab or shrimp meat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/596,254, which is a 371 of PCT/CA04/002090 filed Dec. 8, 2004,claiming the benefit of U.S. Provisional Patent Application No.60/527,752 filed Dec. 9, 2003, all of which are incorporated herein byreference.

FIELD OF THE INVENTION

This application relates to a method of shucking lobster, crab orshrimp, and more particularly to a method for effecting detachment ofthe shells of lobster, crab or shrimp to facilitate their removal.

BACKGROUND OF THE INVENTION

Lobster, crab and shrimp are invertebrates belonging to the class knownas “crustacea”. The skeletons of crustaceans are located on the exteriorsurface of their bodies and are known as exoskeletons. The exoskeletonforms a hard shell which protects the animal from predators. Althoughrigid, the shells of crustaceans are segmented to permit movement andare softer and more flexible than the shells of bivalve mollusks such asclams or oysters.

The shell of the crustacean is attached to the underlying muscle tissueby a continuous series of intracuticle fibres that extend across theentire animal. These intracuticle fibres extend from the surface of themuscle tissue to the outer surface of the shell via pore canals in theshell. This continuous attachment renders it difficult to remove theshell by manual cutting. Accordingly, a variety of processing means havebeen developed to weaken the linkages affixing the shell to the body inorder to facilitate removal of the shells and retrieval of the meatunderneath.

Traditional methods for removing the shells of crustacean shellfish,such as shrimp and lobster, involve cooking the animals prior topeeling. Heat denatures the linkages attaching the exoskeleton to theshellfish meat, thus facilitating removal of the shells. However,following the application of heat, additional means must be employed toseparate the meat from the shell. Manual extraction of the meat istime-consuming and laborious while mechanical means often cause the meatto be minced or flaked, thus limiting its potential applications. Afurther difficulty with using heat to facilitate loosening of the shellis that the shellfish meat underneath inevitably becomes cooked duringthe process. Cooking of the shellfish meat affects both its flavour andits texture thereby preventing the meat from being used in cuisinesrequiring raw ingredients, such as sushi. Cooking represents aparticular problem in the case of lobsters due to the differingthickness in various parts of the lobster's body. Cooking periods ofsufficient length to loosen the shell of the tail of the lobster oftenresult in overcooking of the meat in the smaller sections such as theclaws and the legs. The result is reduced flavour and quality invaluable sections of the animal.

Removal of the shells represents a particular problem in the case oflobster meat which is virtually impossible to extract from its shell inthe raw state. Chefs requiring raw lobster meat for certain dishes willreduce the cooking time as much as possible by blanching live lobstersto loosen the shells. However, blanching fails to effect completeremoval of the shells and still results in some cooking of the surfacemeat. Restaurants which serve fresh lobster typically maintain theanimals in a live state up until the point of cooking and then servethem cooked, but still within the shell. The ability to purchase raw,but deshelled, lobster meat would greatly increase the ease andconvenience of serving a variety of fresh lobster dishes.

In the case of shrimp, a common technique for facilitating removal ofthe shells is to permit the shrimp to “mature” for two to three daysfollowing death. During this period, the shell softens thus renderingthe shrimp easier to peel. However, this method detracts from thefreshness of the shrimp. Accordingly, a need exists for a process tofacilitate removal of the shells of crustacean shellfish without heatingthe animals, and thereby cooking the shellfish meat, or leaving them tomature, thus reducing their freshness.

In recent years, attempts have been made to loosen the shells of rawlobsters by soaking them in chemicals or in enzymes to loosen theconnective tissue attaching the shells to the bodies. U.S. Pat. No.6,235,338 describes a method of removing raw meat from the head-shell ofa crustacean shellfish by immersing the animal in a solution of proteaseenzymes. The same patent also describes an additional method involvingfreezing of the animal followed by vacuum aspiration. However, thesemethods have not delivered consistent results and have not been widelyadopted by the seafood industry.

In recent years, technology has been developed which has enabled foodsto be processed using high pressure treatment. Exposure of foods to highpressure has been most commonly used to eliminate bacteria and otherpathogens. High pressure treatment has been used as a preservationmethod for a variety of different types of foods including meats, fruitsand other products. U.S. Pat. No. 6,426,103 (the '103 patent) issued onJul. 30, 2002, describes the use of high hydrostatic pressure toeliminate pathogenic organisms from raw shellfish. Foods, includingseafoods, subjected to high pressure have been shown to maintain a highquality in their texture, taste and appearance.

In addition to the elimination of pathogens, the '103 Patent describesrelease of the meat of oysters which had been subjected to pressure at aminimum of 25,000 psi for a period of 15 minutes at ambient temperature.A similar effect was observed at higher pressures for shorter periods.Oysters are bivalve mollusks having hard shells consisting of twohalves. The shell of the oyster is attached to a muscle called anadductor muscle. The '103 Patent discloses that, followingpressurization, the adductor muscle connective tissue of the oyster wasdenatured to a gel. As a result, a gap appeared between the two shellhalves and the oyster meat slid out without the need for manual cutting.The '103 Patent does not suggest that high pressure could be used tofacilitate the removal of shells of animals other than oysters.

The physiology of bivalve mollusks is quite distinct from that ofcrustaceans. As can be observed in FIG. 1, the meat of bivalve mollusksis attached to the shell only at the adductor muscle. By contrast, ascan be observed in FIG. 2, the meat of crustacean shellfish is attachedto the shell continuously across the body of the animal. Furthermore,the attachment mechanism in crustacean shellfish is complicated by thepresence of innervations of external tactile sensory hairs that passthrough the shell to the underlying cuticle.

Addressing this point in greater detail, crustaceans such as lobstersand crabs are mobile and hence require muscle structure and functionpermitting movement. This is achieved by complete and continuousattachment of muscle to the crustacean exoskeleton. In contrast,bivalves (e.g. clams, oysters, mussels and scallops) are either sessile(mussels and oysters), or move by extending a muscular foot from theshell (clams) or by propulsion (scallops). Accordingly, whereas bivalvemuscle tissue is attached to the shell only at small discrete pointsrequired to close the shell (adductor muscles) or for shell formation(mantle), the majority of the shell of a crustacean possesses muscleattachments.

In lobsters, particularly, the configuration of muscle attachment ismuch more complex than that in bivalves. Pores are evenly distributedover the surface of the lobster shell. These pores extend through theshell and into the muscle tissue. The resulting complex matrix of poreinvaginations into the muscle tissue of the lobster is partlyresponsible for the difficulty in removing lobster meat from the shellin an uncooked state.

The lobster shell is composed of an epicuticle, procuticle, membranouslayer, epidermis and basement membrane. The muscle tissue lies beneaththe basement membrane. A highly interdigitated intermediate junctionoccurs between the epidermis and the muscle tissue. Within theepidermis, conical hemidesomosomes are formed as invaginations of theapical cell membrane, and intracuticular fibers pass form the conicalhemidesomosomes into the cuticle. Each hemidesomosome joins a muscleattachment fiber, which extends within a pore canal through the cuticleto the outer epicuticle.

In contrast, bivalve shells consist of three layers: a thin outerperiostracum, a mid prismatic layer of aragonite or calcite, and aninner calcareous (nacreous) layer. The middle and inner layers containthin layers of columnar prisms known as myostraca. The mantle andmuscles of the bivalve are attached to the myostraca by strands ofconnective tissue.

The present invention provides a novel method for effecting detachmentof the shells of lobster, crab or shrimp to facilitate their removal. Italso provides seafood products obtained using this method.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method of facilitatingremoval of the shells of lobster, crab or shrimp comprising exposinglobster, crab or shrimp to pressure for a period sufficient to effectdetachment of the meat from the shell.

In another aspect, the invention provides a seafood product whichcontains the meat of a lobster, crab or shrimp, which lobster, crab orshrimp has been exposed to pressure for a period of time sufficient toeffect detachment of the meat from the shell.

In another aspect, the invention provides a seafood product whichcontains the meat of a lobster, crab or shrimp, which meat is uncookedand has not been subjected to chemical or enzymatic treatment to effectthe removal of the shell.

BRIEF DESCRIPTION OF THE DRAWING

Reference will now be made to the drawings, wherein FIG. 1 is a top viewof a lobster, the shaded area illustrating the area where the shell isattached to the meat; and

FIG. 2 depicts a bivalve mollusk, the shaded area illustrating thesingle point of attachment of the shell to the meat at the adductormuscle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A new method for effecting detachment of the shells of lobster, crab orshrimp will now be described in more detail. According to this method,lobster, crab or shrimp are exposed to pressure for a period of timesufficient to detach the shells so that the shellfish meat can be easilyextracted.

Lobster, Crab or Shrimp

The invention has been demonstrated to be useful for removing the shellsof shrimp, and also lobster and crab, while leaving the meatsubstantially intact. The successful application of the methods of theinvention to lobster and crab is particularly surprising given the muchgreater thickness and rigidity of the shells of lobsters and crabsrelative to shrimp. Moreover, the muscle fibers of lobsters and crabsare much stronger than those of shrimp. This results in much highershearing forces during removal of the shells of lobsters and crabs,increasing the difficulty in obtaining intact de-shelled lobster or crabmeat.

The invention may be used with lobster, crab or shrimp which are live ordead, whole or cut into pieces, fresh or frozen. As well, it may becombined with other methods for processing seafood including cooking andflavouring, or chemical, enzymatic or heat treatment.

Methods

Lobster, crab or shrimp are exposed to pressure for a period of timesufficient to effect detachment of the body from the shell. The skilledartisan can vary the time and pressure to obtain best results.Generally, detachment can be effected in short periods of time byapplying pressure of at least about 25,000 psi. Higher pressures, e.g.about 30,000; 35,000, 40,000; 45,000; 50,000; 55,000; 60,000; 65,000;70,000; 75,000; 80,000; 85,000; 90,000; 95,000 or 100,000 psi may alsobe used. Lower pressures, such as about 5,000; 10,000; 15,000; or 20,000psi may also prove to be sufficient in certain cases. Currentlyavailable commercial pressurization equipment is capable of achievingpressures of up to about 100,000 psi, however, pressure greater thanthis, if achieved, would be effective. For shrimp and lobsters, pressureof at least about 25,000 psi is preferred to achieve detachment in ashort period of time. For crab, pressure of at least about 80,000 psi ispreferred to achieve detachment in a short period of time.

The amount of exposure time required varies with the amount of pressureapplied. Specifically, where a higher pressure is used, a shorterexposure time is required. Exposure times of about 15, 30, 45, 60, 75,90, 105, 120, 135, 150, 165 or 180 seconds are typical, although longerexposure times can be used.

Any type of externally applied pressure is suitable for use with thesubject invention including hydrostatic pressure and isostatic pressure.In addition, the subject invention can be used at any temperature.Typically, the temperature of the meat of the lobster, crab or shrimp isbetween about 0° C. and about 100° C. when pressure is applied. It istherefore possible to carry out the method of the subject invention atambient temperature (e.g. about 10° C. to about 30° C., typically about20° C.), or to combine it with cooling or heating of the lobster, crabor shrimp.

Following pressurization, the shells of lobster, crab or shrimp can beeasily separated from the meat using any available means. This caninclude manual removal of the shells, the use of the mechanical devices,vacuum aspiration, water washing or the use of air pressure.

The term “about” is used above in connection with the discussion oftimes, temperatures and pressures, as the skilled person will appreciatethat exact times, temperatures and pressures are not essential orcritical. The term “about” shall be understood to encompass suchvariations in time, temperature and pressure as may be appropriate in aparticular circumstance to effect removal of the shell of a lobster,crab or shrimp and, in any event, shall be understood to encompass ±5%,10%, 15%, 20% or 25% of the stated value.

Apparatus

Any apparatus capable of applying pressure of at least about 25,000 psito the shell of a lobster, crab or shrimp may be used in the methods ofthe invention. However, in some applications equipment capable ofproducing pressure of as little as about 5000 psi may be useful.Preferred is apparatus that produces hydrostatic pressure. There is avariety of different commercially available equipment that is suitablefor use in the methods of the invention including, for example, thehydrostatic pressure equipment described in U.S. Pat. Nos. 6,537,601issued Mar. 25, 2003, 6,426,103 issued Jul. 30, 2002, 6,393,977 issuedMay 28, 2002, and 6,217,435 issued Apr. 17, 2001, all of which areincorporated herein by reference, and which is sold by FlowInternational Corporation (Kent, Wash., USA) under the trademark FRESHERUNDER PRESSURE.

Applications

The bodies of lobster, crab or shrimp which have been detached from theshells using the method of the subject invention provide meat which isdeshelled but uncooked. By the methods of the invention, the meat fromthe various body parts of the lobster, crab or shrimp can be recoveredin a substantially intact form (i.e. whole or large pieces), without themincing or flaking that results from other extraction methods. Since themeat is uncooked, it can be used by restaurants or consumers in seafooddishes which necessitate little or no cooking. The availability of raw,but deshelled, lobster, crab or shrimp offers chefs and consumers theopportunity to prepare a variety of dishes which were previouslyimpossible to prepare.

The deshelled, raw lobster, crab or shrimp can also be used in foodswhich are further processed by e.g. freezing, canning or vacuum sealing.It can also be used in a variety of food products which include seafoodas an ingredient including e.g. breaded seafood, frozen dinners, andsoups.

The invention will now be further illustrated by the followingnon-limiting examples.

Example 1

Lobsters were tested using pressures of 25,000 psi, 30,000 psi, 40,000psi, 50,000 psi, 60,000 psi and 87,000 psi. Following pressurization,the meat of the lobster had completely detached from the shells and, asa consequence, it was possible to easily remove the shells manually.Pressure was retained for a sufficient time period to cause the meat todetach from the shell. At 25,000 psi, approximately 120 seconds wassufficient whereas, at 50,000 psi, 45 seconds was sufficient. Tests wereperformed using both live and dead lobsters with similar resultsobserved for both. The tests were conducted at ambient temperature. Onesurprising observation was that detachment of the meat from the shelloccurred throughout the body of the lobster, with the result that all ofthe meat could be easily and completely removed from the shell.

In order to evaluate the yield of meat recovered following high pressuretreatment, seven different batches of lobster were exposed to highpressure at 35,000 psi for 90 seconds. Yield results are shown inTable 1. As can be observed, the total yield was 29%. Subsequent testsin which the claws, tails and legs of lobsters were isolated showedyields of 54%, 61% and 49% respectively. Lobster meat released from theshells following pressurization treatment showed no evidence of cookingand thus retained the taste and texture of raw lobster meat.

TABLE 1 Total Green Claw in Claw Tail in Tail Legs in Leg Box WeightShell Meat Shell Meat Shell Meat 1  29.6  9.3  7.0  9.4  8.3 1.4 1.1 2 30.5  6.3  0.4  4.9  9.1 1.4 1.1 3  30.6  7.8  2.2  5.6  9.0 1.0 0.0 4 29.3  5.0  5.8  3.5  0.0 1.5 0.0 5  30.6  8.0  7.3  8.9  0.0 2.5 0.0 6 29.3  3.1  0.0  5.0  0.0 0.0 0.0 box 7 hardshell  26.3  8.6  3.9  6.1 4.2 1.8 0.4 Total kgs 206.2 48.2 26.6 43.4 30.6 9.5 2.7 AV meat 29.0%yield

Example 2

Cold water shrimp were exposed to pressures ranging from 32,500 psi to47,500 psi for periods ranging from about 15 seconds to about 120seconds. The tests were conducted at ambient temperature. Followingpressurization, the shrimp were peeled to remove the shells, bothmanually and using mechanical shrimp peeling equipment. Test resultsshowed excellent detachment of shells from the bodies of shrimp whichgreatly facilitated both manual and mechanical removal of the shells.The method was effective for both live shrimp and dead shrimp.

Example 3

Jonah crab and snow crab were exposed to pressure at 87,000 psi forabout 90 seconds at ambient temperature. Following pressurization, theshells of both jonah crab and snow crab were partially released from thebodies. Some manual cutting was required to remove the shells.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present invention is not entitled to antedate suchpublication by virtue of prior invention.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it is readily apparent to those of ordinary skill in theart in light of the teachings of this invention that certain changes andmodifications may be made thereto without departing from the spirit orscope of the appended claims.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural reference unless the contextclearly dictates otherwise. Unless defined otherwise all technical andscientific terms used herein have the same meaning as commonlyunderstood to one of ordinary skill in the art to which this inventionbelongs.

1. A method of facilitating the removal of the shell of a crustaceanshellfish selected from the group consisting of lobster, crab andshrimp, comprising: exposing the crustacean shellfish to pressure for aperiod of time sufficient to effect detachment of the meat from theshell.
 2. The method of claim 1, wherein the pressure is at least about25,000; 30,000; 35,000, 40,000; 45,000; 50,000; 55,000; 60,000; 65,000;70,000; 75,000; 80,000; 85,000; 90,000; 95,000 or 100,000 psi.
 3. Themethod of claim 1, wherein the pressure is maintained for a period of atleast about 15 seconds.
 4. The method of claim 1, wherein the pressureis maintained for a period of at least about 15, 30, 45, 60, 75, 90,105, 120, 135, 150, 165 or 180 seconds.
 5. The method of claim 1,wherein said exposing to pressure is at a temperature of between about10° C. and about 30° C.
 6. The method of claim 1, wherein said pressureis hydrostatic pressure.
 7. The method of claim 1, further comprisingheat treatment or chemical or enzymatic treatment of said crustaceanshellfish before, during or after said exposing to pressure.
 8. Themethod of claim 1, wherein said crustacean shellfish is not exposed toheat treatment or chemical or enzymatic treatment before, during orafter said exposing to pressure.
 9. The method of claim 1, wherein thecrustacean shellfish is lobster.
 10. The method of claim 9, wherein thetotal yield of lobster meat (total weight of claw, tail and legmeat/total green weight of lobster) is at least about 29%.
 11. A seafoodproduct comprising the meat of a crustacean shellfish selected from thegroup consisting of lobster, crab and shrimp, which crustacean shellfishhas been subjected to the method of claim 1 to facilitate removal of theshell of said crustacean shellfish.
 12. The seafood product of claim 11,wherein the crustacean shellfish is lobster.
 13. A seafood productcomprising the meat of a crustacean shellfish selected from the groupconsisting of lobster, crab and shrimp, which meat is uncooked and hasnot been subjected to enzymatic or chemical treatment to effect removalof the shell of the crustacean shellfish.
 14. The seafood product ofclaim 13, wherein the crustacean shellfish is lobster.
 15. The seafoodproduct of claim 14, comprising the meat of a lobster claw with theshell removed, the meat having a yield of at least about 54% (weightclaw meat/weight of claw in shell).
 16. The seafood product of claim 14,comprising the meat of a lobster tail with the shell removed, the meathaving a yield of at least about 61% (weight tail meat/weight of tail inshell).
 17. The seafood product of claim 14, comprising the meat of alobster leg with the shell removed, the meat having a yield of at leastabout 49% (weight leg meat/weight of leg in shell).
 18. The seafoodproduct of claim 13, wherein the meat is released from the shell in asubstantially intact state, without mincing or flaking.